At present, computer output data are printed out with the aid of alphanumeric printers using the same character face and size. Such a simplified printout of textual information does not always satisfy the requirements of information services in rapid printing of such matter as reference books, catalogues, promotional booklets and other documents which are normally printed with different type faces and sizes. To meet this requirement, the initial information printed on alphanumeric printers must be reprinted by conventional printing means, which takes much more time.
In conventional printing, when text data processing systems being photocomposition are employed, the initial punched tape has to be printed out for editorial revision and proof reading. The use for this purpose of alphanumeric printers with simplified characters does not fully solve the problem because of the limited type face which does not tell much about the typography of the future publication. Nor is the use of automatic photocomposing machines always possible for the purpose because of the prohibitively high cost of the photographic materials on which the image is produced.
Known in the art is an electrographic photocomposing machine (cf. U.S. Pat. No. 3,768,384; Cl. 95-4,5; 1973) comprising a rotary type carrier provided with a flashtube and a control unit, a photographic unit and a driven line forming mechanism, the latter two being arranged in series downstream of the type carrier along the beam produced by the flashtube. The photocomposing machine also comprises an electrophotographic section including a cylindrical intermediate image carrier optically associated with the line forming mechanism and provided with its own drive, a charging device arranged in direct proximity to the intermediate image carrier in the latent image forming zone and provided with a lamp for exposure of the intermediate image carrier, and a device for developing the latent image, contiguous with the surface of the intermediate image carrier and oriented in the direction of its rotation, downstream of the charging device. The electrophotographic section also includes a device for transferring the powder image, provided with a driven paper feed system, ensuring mechanical contact between the paper web and the intermediate image carrier, and arranged downstream of the latent image developing device in the direction of rotation of the intermediate image carrier. In addition, the electrophotographic section comprises a unit for fixing the powder image onto the paper with heaters arranged near the paper web on the side of the powder image and downstream of the powder image transferring device in the direction of paper motion, and a device for cleaning the intermediate image carrier, located downstream of the powder image transferring means in the direction of rotation of the intermediate image carrier. The machine also comprises a computer electrically associated with the drive of the line forming mechanism and coupled to the control unit of the flashtube.
In this prior art photocomposing machine, the drives of the line forming mechanism, cylindrical intermediate image carrier and paper feed system are electric motors with a constant rotational speed.
In such a machine, the text is formed character by character on the surface of the regularly rotating intermediate image carrier, following instructions initiated by the computer unit, from the disk type carrier with the aid of the flashtube, photographic unit and line forming mechanism.
The photographic unit is essentially a chain transporter with optical carriages each made up of a lens and a mirror. The transporter moves at an angle to the generatrix of the cylindrical intermediate image carrier, determined by the ratio of the carriage speed to that of the intermediate image carrier.
Obviously, since regularly rotating type carrier, intermediate image carrier and transporter with carriages are used in the machine, the actual spacings between characters (approaches) will differ from the design values because of the fact that, after a carriage has moved an amount of space corresponding to a given position of the character in the text line, additional (uncontrollable) time is required for the character selected on the type carrier to approach the exposure zone, during which the carriage and intermediate image carrier continue to move.
Also, in the prior art electrographic photocomposing machine, the presence of the above regularly rotating components makes it necessary to keep the heaters of the unit for fixing the powder image onto the paper constantly on, which does not provide for the desired quality of the electrographic prints. When tubular heaters are used, heat is transferred from the latter to the prints through air, which leads to heating both the powder image and paper to high image fixing temperatures with the result that the paper may warp and its mechanical properties may be impaired. When high-temperature heaters are used, heat is transferred by way of radiation, which may lead to the image burning through the paper, i.e. characters may appear on the back side of the paper. This results from the fact that, unlike the powder, the paper reflects, during fixing of the powder image, most of the infrared radiation and has no time to be heated. The burn-through occurs as a result of heat being transferred from the heated powder to the paper portions corresponding in shape to respective characters.
It should also be noted that the prior art machine makes it difficult to compose complex texts and sizes since this requires time and can only be provided by stopping the intermediate image carrier, paper feed system and chain transporter with carriages. Frequent stops of these components involve, first of all, considerable forces of inertia to be defeated in the mechanisms of their drives and, secondly, fail to provide for even fixing of the powder image on the paper in the respective unit with the heaters being constantly on because of the different times of their thermal action of the powder image.
Thus, the design of the unit for fixing the powder image on paper with the heaters being constantly on and the impossibility of composing characters of different faces and sizes in the prior art electrographic photocomposing machine do not provide for a sufficiently high quality of electrographic prints.